15kW solar systems: A great size for large homes & businesses

A 15kW solar system for Kennards Hire in Rutherford, NSW.

15kW solar systems are a great system size for homes with high levels of energy consumption or businesses with small to middling energy needs – provided that they have sufficient roof space to install one. This article takes you through (almost) everything you might want to know about 15kW solar systems, including how much space they take up, how much they cost, and how much energy you can expect them to produce. It also touches on whether a 15kW system is a good investment for your home or business.


How many panels & how much roof space for a 15kW solar system?

A modern-day 15kW solar system will be comprised of between about 37-45 panels and will require about 75-90 m2 of roof space, depending on the wattage of the panels (which are typically between 330-400W each). A typical residential solar panel is 1.7 metre by 1 metre. This means that for most homes, a 15kW solar system will not be an option unless it is ground-mounted.

15kW Solar Panel Systems – roof space and number of Panels
Solar panel watt rating 330W 400W
Approximate number of panels 45 37
Approximate roof area required 75m2 90m2



How much does a 15kW solar system cost?

Australia is home to some of the lowest solar installation prices in the world, and 15kW solar systems – because of their size – frequently offer some of the best value of any solar PV system size. You can view current indicative solar system prices on the Solar Choice Price Index (although 15kW is not yet a regular feature in our monthly Solar PV Price Index, 10kW has been included for a number of years now.)

According to Solar Choice’s own data, as of March 2022 the average cost of a fully installed 15kW solar panel system in Australia is around $0.84 per watt – or about $12,600 after deducting the STC rebate and including GST.

The chart below give a rough idea of what average prices for 15kW solar system look like in (most of) Australia’s capital cities.

Average 15kW solar system costs based on Solar Choice Price Index

City Out of pocket cost (incl GST and incentives) Cost per watt installed
Adelaide, SA $12,000 $0.80
Brisbane, QLD $12,000 $0.80
Canberra, ACT $12,900 $0.86
Hobart, TAS $15,600 $1.04
Melbourne, VIC $12,150 $0.81
Sydney, NSW $11,700 $0.78
Perth, WA $11,400 $0.76
Average: $12,600 $0.84


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How much energy does a 15kW solar system produce?

Depending a number of factors, the actual power output of a 15kW solar panel system will vary. These variables include:

The table below gives indicative figures for how many kilowatt-hours of energy a north-facing 15kW solar system will generate per day (on average throughout the year) in Australia’s capital cities.

 Indicative daily 15kW solar panel output by capital city

City Average Daily Production Estimated Annual Production
Adelaide 58 kWh per day 21,079 kWh
Brisbane 60 kWh per day 21,900 kWh
Canberra 58 kWh per day 21,079 kWh
Darwin 66 kWh per day 24,090 kWh
Hobart 47 kWh per day 16,973 kWh
Melbourne 50 kWh per day 18,341 kWh
Perth 63 kWh per day 22,995 kWh
Sydney 54 kWh per day 19,710 kWh


  • Calculations completed via PVWatts using sunlight data from the Bureau of Meteorology
  • Conservatively assumes that the systems efficiency is 75%
  • Assumes the solar panels a mounted at a 30 degree angle to the north


Is a 15kW solar system right for your home or business?

As you can guess by the amount of roof space required, a 15kW is a serious amount of solar for the ordinary home – and in many cases it will be too much. In most cases, it will only be appropriate if you’re using over 50kWh of energy on average per day – a number much more likely to apply to a business than a home. It may also be a good size choice for homes who have low electricity consumption and want to go off-grid (see: “Can I go off-grid with a 10kW solar system?“)

Because of the complexity involved (not to mention the cost) we recommend that you have the numbers crunched in detail before deciding to go ahead with a 15kW solar system. You can experiment with the numbers yourself with our Simple Solar System Sizing Estimator, check out our Solar Payback & ROI Estimator Tool or request a free, customised business case analysis from our engineering team based on your electricity bills.

Also keep in mind that the Distributed Network Service Provider (DNSP) who is the company who owns the poles and wires in your area may have particular rules on what can be connected and what systems are permitted to export power. Often for single phase connections the limit is a 5kVA inverter which can accommodate 6.6kW of solar panels.

An additional consideration is that many of the electricity retailers feed in tariff plans are capped at systems with a 10kW inverter. See a summary of the latest plans on this feed in tariff page.

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Is a 15kW solar system worth it?

These days solar feed-in tariff credits are a secondary benefit from having a solar system installed. Instead,  you’ll derive the most value out of your self-generated solar energy by ‘self-consuming‘ it – using as much energy as possible directly. Because solar feed-in tariff rates are generally lower than what you’ll pay for energy from the grid, the more solar energy you use yourself, the more you’ll save; meanwhile, the excess solar will flow into the grid and earn you credits which help to reduce your overall bill.

Payback Period & IRR for 15kW solar systems

The table below takes a look at payback times and internal rate of return (IRR) for those who install a 15kW solar system in select cities at two rates of self-consumption – 40% and 70%. Although these rates are high for most ordinary households with solar (typically more like 20-40%), we assume that anyone who goes ahead with a system in the 15kW range has done their research and ensured that a higher degree of their solar energy will go directly to their local energy demand (as opposed to into the grid). If you manage to achieve even higher self-consumption rates, the returns will look even more favourable.

Please note that we’ve assumed that the system is eligible for a solar feed-in tariff – which depends on the electricity retailer and the network rules.

Indicative payback periods for 15kW solar panel systems

15kW System Cost Electricity Price Feed in Rate Self Consumption Rate IRR Annual Savings Payback Period (Years)
Sydney $11,700 25c 7c 30% 21% $2,391 4.8 years
60% 31% $3,516 3.3 years
Brisbane $12,000 18c 5c 30% 15% $1,840 6.4 years
60% 23% $2,652 4.4 years
Melbourne $12,150 27.5c 6c 30% 20% $2,327 5.1 years
60% 31% $3,655 3.3 years
Perth $11,400 28.8c 5c 30% 23% $2,522 4.4 years
60% 36% $3,981 2.8 years
Adelaide $12,000 29c 9c 30% 25% $2,982 4.0 years
60% 36% $4,228 2.8 years
Hobart $15,600 27c 8.5c 30% 16% $2,462 6.2 years
60% 24% $3,627 4.2 years
Canberra $12,900 20c 7c 30% 17% $2,159 5.9 years
60% 24% $2,984 4.2 years
Darwin $20,505 26c 8c 30% 15% $3,018 6.7 years
60% 21% $4,150 4.8 years


  • Assumes the average daily energy usage is 50 kWh per day (very high for residential use)
  • The prices are based on the latest Solar Choice Price Index
  • Self-consumption rates of 30% (low) and 60% (very high) have been selected as examples only and as you can see are very important to the financial outcome

Calculate indicative ROI & payback periods for 15kW solar systems

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